Not much to go on here but it sounds like you have it set to the wrong source. When you say cable are you using a cable box or is the cable coax directly plugged into the TV? If it's a cable box then you should use the HDMI connection with an HDMI cable and use the box to change channels. If it is a cable directly connected with coax then you should use TV or antenna as your source.
With a direct connection you probably won't get 1080p HD or 4K UHD pictures, most likely 720p, since that usually requires a cable box and an upgrade tier.